Technical Field
The present disclosure relates to an apparatus for detecting an occurrence of a creeping of radar waves by using a result of transmission/reception of radar waves.
Description of the Related Art
Conventionally, a radar apparatus mounted on a vehicle, detecting a target based on a result of transmission/reception of the radar waves is known.
For example, Japanese Patent Application Laid-Open Publication Number 2004-330890 discloses a radar apparatus in which radar waves are transmitted at every measurement cycle and a distance (hereinafter referred to detected distance) to the target (e.g., preceding vehicle) from which the radar waves are reflected is detected based on an elapsed time from when the radar waves are transmitted to when the apparatus receives the incoming waves.
In a radar apparatus, when creeping occurs, a problem arises that the radar apparatus erroneously detects a distance longer than a distance from the back end of the preceding vehicle to be the detected distance. It is noted that creeping is a phenomena where radar waves get under the chassis of the preceding vehicle so that the radar apparatus erroneously detects a distance up to a front part of the preceding vehicle rather than the back end of the preceding vehicle, to be the detected distance.
In other words, as shown in FIG. 6A, the radar waves are usually reflected at the back end of the preceding vehicle so that the radar apparatus is able to detect the distance up to the back end of the preceding vehicle as a detected distance. However, as shown in FIG. 6B, when the preceding vehicle is a heavy truck having high vehicle height and the distance between the present vehicle (vehicle where the radar apparatus is mounted) and the preceding vehicle is close, the radar waves get under the chassis of the preceding vehicle depending on the height of location where the radar apparatus is mounted in the vehicle height direction. In this case, since the radar waves are reflected at a front part of the preceding vehicle (e.g., drive shaft) rather than the back end thereof, the radar apparatus detects the distance up to the front part thereof to be the detected distance.
To solve the above-described problem, the radar apparatus disclosed by the above-described patent document determines that the creeping has occurred when a difference among detected distances detected during consecutive measurement periods with respect to the time axis (hereinafter referred to distance variation) increases to be larger than or equal to a predetermined value set in advance.
Generally, a vehicle running on the road repeatedly accelerates/decelerates. Hence, when the vehicle repeatedly accelerates and decelerates, the real distance between the present vehicle on which the radar apparatus is mounted and the preceding vehicle varies with respect to the time axis every time when the vehicle accelerates or decelerates. Also, the detected distance detected by the radar apparatus varies with respect to the time axis as well.
In this case, when the distance variation increases to be larger than or equal to the predetermined threshold, the following problem arises. That is, although the real distance between the present vehicle and the preceding vehicle varies, the radar apparatus according to the above-described patent document erroneously determines that creeping has occurred.
In other words, according to radar apparatuses in the related art, there is a concern that an accuracy of detecting whether or not the creeping has occurred is low.